Bring a large pot of water to a boil. Add a generous pinch of salt, then add pasta and cook just to al dente, according to package directions. Drain and set aside.

While the pasta cooks, warm a large skillet over medium-high heat. Add oil and butter. When butter has melted, add onions and cook for 4-5 minutes, until very tender.

Add the mushrooms and Worcestershire sauce. Sauté for another 5-6 minutes. As they cook, the mushrooms should release some liquid, dry out again, and develop a rich brown color.

Add garlic and thyme. Cook for about 30 seconds, just until fragrant. Stir in the flour and cook for 1 minute more, just until it turns slightly brown.

Whisk in the broth, then let the mixture simmer for 2-3 minutes. The sauce should smooth out and thicken slightly.

Toss the sauce with or serve on top of drained pasta. Garnish with a sprinkle of fresh parsley or thyme as desired.